The present disclosure relates to a heat radiator having a circuit substrate and a heat sink. The present disclosure also relates to a method for manufacturing the heat radiator.
A conventionally known semiconductor apparatus has a ceramic substrate, which is an insulation substrate, and a front metal plate, which is joined to the front surface of the ceramic substrate and serves as a wiring layer, and a back metal plate joined to the back of the ceramic substrate. A semiconductor device is joined to the front metal plate. A heat sink, which radiates heat generated by the semiconductor device, is joined to the back metal plate. Heat generated by the semiconductor device during operation of the semiconductor apparatus is radiated through the heat sink. The heat radiating performance of the heat sink is desired to be maintained for an extended period of time. However, depending on the use conditions for the semiconductor apparatus, cracks may form at the joint portions between the ceramic substrate and the back metal plate due to thermal stress caused by the difference in the coefficient of linear expansion between the insulation substrate and the heat sink. Also, extension of cracks can cause the back metal plate to peel off the ceramic substrate, which can lower the heat radiating performance.
In this regard, Japanese Laid-Open Patent Publication No. 2006-294699, for example, discloses a semiconductor apparatus that has a stress relaxation member, which is located between a back metal plate and a heat sink. According to the document, an aluminum plate is used as a stress relaxation member, in which multiple through holes are formed to extend in the direction of the thickness. This structure relaxes thermal stress when the semiconductor apparatus operates.
In the semiconductor apparatus disclosed in the document, an air layer is formed between the back metal plate and the heat sink because of the through holes formed in the aluminum plate. Since air has a lower thermal conductivity than aluminum, the heat generated by the semiconductor device reaches the heat sink after bypassing parts of the aluminum plate in which the through holes are formed. That is, the through holes hinder diffusion of the heat generated by the semiconductor device. In other words, the structure hinders transmission of heat to the heat sink, and lowers the cooling efficiency.
Accordingly, it is an objective of the present disclosure to provide a heat radiator that promotes diffusion of heat generated by a semiconductor device while relaxing thermal stress generated during operation of a semiconductor apparatus. The present disclosure also provides a method for manufacturing the heat radiator.